A Flexible Fuel Vehicle (FFV) is a vehicle which can operate with a fuel mixture comprising a first and a second fuel. The first fuel is for example gasoline and the second fuel is for example ethanol. A gasoline/ethanol mixture is for example offered at appropriate filling stations, it being possible for the proportion of ethanol to lie between 0% and 100%. Depending on the composition of the fuel, a different quantity of fresh air is required for complete combustion of a predefined quantity of fuel.
To regulate the injection a lambda regulation is for example used, in order to achieve a combustion with a desired ratio between fuel and air. The lambda regulation must also take account here of the fuel mixture comprising a first and a second fuel. In the case of a fuel which for example consists only of gasoline, the air requirement of the fuel for a complete combustion is in the region of 14.6 kilograms of air per kilogram of fuel. In the case of a fuel which for example consists only of ethanol, only 9 kilograms of air are required per kilogram of ethanol for a complete combustion. Therefore it is necessary to know the mixture of the fuel, i.e. the proportion of the first and the proportion of the second fuel, in order to be able to adjust the ratio between fuel and air required for complete combustion. Furthermore it is known for changes occurring in the lambda signal to be assigned to a changed mixture of the fuel after fueling the vehicle. To this end a corresponding adaptation value is adjusted during the regulation such that the lambda signal again corresponds to a target value.